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Editors' Choice

Remote sensing for analyzing smallholder farm yields

Pamela J. Hines

Remotely sensed estimates of nutrient value reveal differences among local farms in Kenya.

PHOTO: HAILEY TUCKER/ONE ACRE FUND

Smallholder farmers are key to local food security, but their productivity, or lack thereof, is buried when agricultural statistics are discussed at the scale of regions and nations. Household surveys are hampered by errors in self-reporting, and on-the-ground field surveys are constrained by limited personnel. Burke and Lobell combined high-resolution satellite imagery (at the scale of 1 m) with ground-truthed data to estimate yields from maize agriculture in western Kenya, where many of the fields are less than half an acre in size and irregularly shaped. Measurements of canopy greenness captured evidence of nutrient deficiencies. Productivity differed by as much as threefold even between neighboring plots, suggesting opportunities for yield improvement through changes in field management.

Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1616919114 (2017).

Geophysics

Sand-driven magnetic field

Brent Grocholski

Earth's magnetic field is due to convection of its liquid iron-nickel core, which also contains an unknown amount of lighter elements such as silicon, oxygen, and sulfur. Hirose et al. performed experiments that show that silica unexpectedly crystallizes out of a liquid iron alloy at high pressures and temperatures. This discovery identifies a source of compositional buoyancy that would have driven the convection needed for a magnetic field very far back in Earth's history. It also sets a limit on how much silicon and oxygen remain in the outer core today.

Nature 10.1038/nature21367 (2017).

Psychology

Microaggression actions outpace evidence

Brad Wible

Efforts to combat prejudice in workplaces and on campuses by targeting microaggressions lack solid foundations in psychological research. Lilienfeld, who supports microaggression research, surveyed evidence and identified 18 research priorities—for example, better define what is not a microaggression, and do not confound the frequency of microaggressions with the subjective distress that they evoke. He suggests tempering assertions about causal links between microaggressions and adverse mental health and proposes a moratorium on intervention programs that may create more problems than they solve.

Perspect. Psychol. Sci. 10.1177/1745691616659391 (2017).

Malaria

Softening up your target

Stella M. Hurtley

During infection, malaria parasites must invade erythrocytes. Erythrocytes are flexible cells that can easily deform to make it through the tight spaces of the vasculature, but they are nevertheless fortified by a membrane-associated, spectrin-based cytoskeleton. Sisquella et al. examined the invasion process to see how the parasite manages to gain access to the erythrocyte cytoplasm. They found that early interactions between the parasite and the erythrocyte increase the local deformability of the erythrocyte membrane, promoting invasion. The parasite triggers a signaling cascade within the erythrocyte that “loosens up” its cytoskeleton. Blocking this signaling inhibited the ability of the parasites to invade.

eLife 10.7554/eLife.21083 (2017).

Nanomaterials

Restacking the deck

Phil Szuromi

Screw dislocations affect the geometry of WSe2 nanoplates.

PHOTOS: MELINDA J. SHEARER

The properties of two-dimensional sheets of layered transition metal dichalcogenides such as tungsten diselenide (WSe2) depend on how the layers stack. For example, the more common 2H phase has a two-layer AB repeat and is centrosymmetric, but the rare 3R phase has a three-layer ABC repeat and different electronic properties because it is noncentrosymmetric. Shearer et al. grew WSe2 nanoplates through chemical vapor deposition that had screw dislocations. A triangular dislocation grew noncentrosymmetric layers, a hexagonal dislocation grew centrosymmetric layers, and mixed dislocations grew weakly noncentrosymmetric layers. They explored the changes in properties with stacking, such as strong second-harmonic generation with the noncentrosymmetric material.

J. Am. Chem. Soc. 10.1021/jacs.6b12559 (2017).

Neurodevelopment

Love hormones and mental health

Megan Eldred

Oxytocin, also known as the love hormone, plays vital roles in childbirth and social bonding. It is also crucial in aiding the correct wiring of certain neuronal circuits in the brain during development, and altered oxytocin signaling has been implicated in neuropsychiatric conditions such as autism spectrum disorder. Ripamonti et al. looked deeper and discovered that a surge of maternal oxytocin right before childbirth is required for the priming of excitatory hippocampal neurons, which are typically involved in memory formation and anxiety regulation. In this process, oxytocin regulates dendritic branching, synapse formation, and synaptic transmission, allowing for the synchronicity of the neuronal network. Without this, the balance of excitatory and inhibitory signals is disrupted, which can lead to neurobehavioral disorders.

eLife 10.7554/eLife.22466 (2017).

Neuroscience

Fine-scale structure in higher brain areas

Peter Stern

The prefrontal cortex of the brain is involved in higher-order cognitive processes, including attention, decision-making, and goal-directed action. At present, we do not know how abstract context is represented in the prefrontal cortex, whether there are subregions, and, if so, how they might be organized. Waskom and Wagner used high-resolution brain scanning while subjects performed tasks that demanded goal-directed behavior. Multivariate signal–decoding techniques and examination of spontaneous activity correlations demonstrated the existence of stable networks of subregions within this brain area. Abstract cognitive representations thus emerge from an intrinsic functional organization in the human prefrontal cortex.